Light mixer



R. A. CLAPP June 2, 1964 LIGHT MIXER Filed July s, 1966 2 Sheets-Sheet l 'FIGQ2 INVENTOR.

ATTORNEYS June 2, 1964 R. A. CLAPP 3,135,471

LIGHT MIXER Filed July 5, 1960 2 Sheets-Sheet 2 I FIG. 7

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INVENTOR ROY A. CLAPP ATTORNEYS United States Patent 3,135,471 LIGHT MIXER Roy A- Clapp, Minneapolis, Minn., assignor to Pairo Corporation, Minneapolis, Minn., a corporation of Delaware Filed July 5, 1969, Ser. No. 40,735 2 Claims. (Cl. 240--3.1)

The herein disclosed invention relates to light mixers and has for an object to provide a mixer producing photographic illuminant having predetermined spectral content with components of selected intensity..

Another object of the invention resides in providing means for readily and eflectively varying the intensity of the components.

I A still further object of the invention resides in providing means for producing a light having the desired characteristics for color photographic printing and at the same time without producing visual glare.

An object of the invention resides in providing means for producing a highly diffused and uniform light.

Another object of the invention resides in providing a highly eflicient light mixer producing a high luminosity from a given amount of light flux.

An object of the invention resides in providing a light mixer having an enclosure in theform of a truncated pyramid provided with a diffuse highly reflecting inner surface.

Another object of the invention resides in providing the light mixer with an emission opening at the smaller end of the lateral wall structure thereof and in providing the lateral wall structure with inlet ports.

A. still further object of the invention resides in arranging the light sources exteriorly of the enclosure adjacent the ports and in mounting an elipsoidal reflector in back of each light source and an annular spheroidal reflector between the light source and the, enclosure.

Other objects of the invention reside in the novel combination and arrangement of parts and in the details of construction hereinafter illustrated and/or described.

In the drawings;

FIGURE 1 is a plan view of a light mixer illustrating an embodiment of the invention.

FIGURE 2 is an elevational view of the structure shown in FIGURE 1. with the housing and one of the lamp assemblies removed.

FIGURE 3 is a perspective View of the enclosure detached from the remaining structure.

FIGURE 4 is a fragmentary elevational sectional view taken on line 4-4 of FIGURE 1.

FIGURE 5 is an elevational cross-sectional view taken on line 5-5 of FIGURE 4.

FIGURE 6 is a perspective view of one of the light directors.

FIGURE 7 is an elevational view of the structure shown in FIGURE 6.

The invention is mounted on a base 10 best shown in FIGURES 1, 2, and 4. This base comprises a table 11, a bottom 12, and end walls 13 and 14, the side and end walls are permanently secured together and have a flange 15 extending inwardly therefrom and about the upper edges of the said walls. Table 11 overlies the flange 15 and is secured thereto by means of screws 16. By means of this construction, a chamber 17 is formed within the base 10.

Mounted on the table 11 is a light-mixing enclosure 20, which is in the shape of a truncated, right pyramid. This enclosure has side walls 21 and end walls 22. The enclosure is of smaller dimensions than the table 11 to leave marginal portions 23 and 24 between the side and end walls 21 and 22 and the edges of the table 11.

notches 47 on opposite sides thereof.

Extending across the lower edges of the side and end walls 21 and 22 is a bottom wall 25, which is permanently secured thereto. The walls 21 have formed therein, two light ports 26 and the wall 22 have each formed in them a single light port 27. These light ports are located about half way between the bottom wall 25 and the upper edges of said walls and are arranged about the perimeter of the enclosure in a manner to equally distribute light to all of the inner surfaces 28 of the enclosure. Formed on the inner surfaces 28 of the walls 23, 24, and 25 is a difluse, highly reflective coating 29. This coating may consist of several coats ofwhite acrylic latex paint which dries with a matte finish found to be highly effective in reflecting and diffusing light impinging thereon.

The upper portion of the enclosure is open to' provide a light emission opening indicated by the reference numeral 31. A light diffusing plate 32 covers this opening and is removably mounted in a frame 33 secured to the upper ends of the walls 21 and 22.

Opposite'each of the light ports 26 and 27 are mount- I ed on the marginal portions 23 and 24 of the table 11 of base 10 light sources 40, which are identical in construction. Only one of these light sources will be described in detail and is best shown in FIGURES 1, 2, and 4. This light source includes an electric light bulb 41, which is mounted in a light socket 42. This socket is attached to the table 11 by means of screws 43. The filament 44 of the light bulb 41 is located opposite the light port 27 and outwardly of the wall 22. At the rear of the light bulb 41 is providedan elipsoidal reflector 45, which is located at a position such that one of its foci is at the filament 44 of light bulb 41 which therefore produces an image of the filament at its other focus which is in the vicinity of the center of the port 27. This reflector has a flange 46 extending partially about the outer circumference of the same and which is formed with The reflector is supported on a yoke 48 attached to the table 11 by means of screws 49. This yoke has cars 51 which are received in the notches 47. A leaf spring 52 is secured to table 11 by means of a screw 53 and presses lightly on the reflector 44 to urge the same toward said yoke and maintain said reflector in engagement with the'ears 51. The upper and lower portion of reflector 45 have openings 54 and 55 therein which provide ventilation for the light bulb 41. In addition, opening 55 receives the light socket 42 and is of a suitable size to permit the removal of the reflector 45 while the light bulb 41 is in position to permit the replacing of light bulbs when required.

In addition to the reflector 45, a second reflector 56 is employed which has a reflecting surface 57 spherical in form and whose center is located at the light bulb filament 44. This reflector is turned in the opposite direction from the reflector 45 and is formed with a flange 57 similarly constructed to the flange 46. This flange overlies the flange 46 and is also notched to receive the cars 51. Spring 52 holds both of the reflectors 45 and 56 detachably mounted on the yoke 48. The reflector 56 has an outlet opening 58 through which the light produced by the light bulb 41 passes through port 27 and into the interior of the light mixing enclosure 20. At the locality of the opening 58 and attached to a bracket 61 is a holder 62 for a heat absorbing filter 66. This filter covers the opening 58 in the reflector 56. This bracket is attached to the table 11 by means of screws 63. Mounted on the wall 22 of enclosure 20 is a holder 64 for a color screen 65 and through which the light emanating from the heat absorbing filter 66 passes. These color screens transmit certain selected portions of the light spectrum and which differ from one another. There are preferably three types of filters, one for each emulsion layer of the sensitized photographic material and in the instant case there are two filters of each kind. These filters are preferably red, green, and blue.

The light on entering the interior of the light mixing enclosure 20 is dispensed by means of light directors 67,

each of which has angularly disposed reflectors 81 preferably specular issuing outwardly from a base 82, and which have openings 68 in the center of said bases. The bases 82 are attached to the walls 21 and 22' of the enclosure 20 with the openings 68 overlying the light ports 26 and through which part of the light passes to the opposite walls. The remainder of the light is directed to the adjacent walls of the enclosure by the reflectors 31.

If desired, light directors in the form of prisms or negative lenses may be used in place of the reflectors. In this manner the light leaving the mixing enclosure through the light emission opening 31 is uniformly mixed and contains the desired light components for the proper printing of the color sensitized material. The light,-on leaving the mixing enclosure, passes through the diffusing plate 32 and through the negative which is held in a negative holder 69 overlying frame 33 and is highly diffused.

To prevent overheating of the various parts of the light mixer, the base is constructed hollow to provide the chamber 17 within the same. Extending through the table 11 andadjacent the lamp sockets, are openings 18 which communicate with said chamber. A blower 19, attached to the bottom 12 of said base, delivers cool air into chamber 17 and from which it is discharged through the openings 18 in table 11 and about the light bulbs 41 to cool the same.

The entire light mixer may be enclosed within a case 73, best shown in FIGURES 2 and 5. This case has a top 74 and side and end walls 75 and '76 depending therefrom. These walls overlie the walls 13 and 14 of base 10 and are secured thereto by means of screws 77. The top 74 of this case has a light emission opening '78 therein which registers with the light emission opening 31 in the light mixing enclosure 20. In addition ventilating openings 79 are formed in the walls 75 and 76. A

negative holder 69 is mounted on the top 74 and holds the negative in proper position to receive the light passing through the diffusing plate 32.

If desired, contact prints may be made by placing the sensitized paper upon the negative 69. If enlargements are preferred, an enlarger 70 may be employed. The objective lens 71 of such an enlarger, together with a portion of the bellows 72, have been shown in FIGURE 2 in proper relation to the diffusing plate 32.

The method of using the invention is as follows: It is well known that color printing material is sensitive to three approximately equal portions of the spectrum. Howeventhere is not a sharp cut off between each of these portions and over laps between the portions exist.

the spectrum which causes the degrading of the denoted colors. It has been found that the following filters meet with the requirements:

(1) Wratten No. 98 which transmits blue in the spectral range of 400 to 490 milli-microns.

(2) Wratten No. 99 which transmits green in the range of 520 to 600 milli-microns.

(3) Wratten No. 29 which transmits red in thef spectral range of 610 milli-micronsto beyond 700 milli-microns.

In the printing of the sensitized'material, the intensity of the individual light sources may be varied to conform to the color requirements of the negatives and to the type of material used, or the length of exposure of each light source may be adjusted to produce the desired results.

The advantages of the invention are manifest. lmproved color saturation is attained with the instant invention. A highly diffused light is produced by means of which defectsin printing due to scratches and other defects in the negative are rendered less noticeable. The apparatus is highly efiicient. Every portion of the negative is uniformly illuminated. The device is inexpensive 7 to manufacture and will not readily get out of order,

there being no moving parts.

Changes in the specific form of the invention, as herein described, may be made within the scope of what is claimed without departing from the spirit of the invention.

Having described the invention, what is claimed as new and desired to be protected by Letters Patent is:

1. A light mixer comprising a hollow enclosure in the form of a truncated pyramid having an end wall and lateral wall connected thereto defining a mixing chamber, said walls having interior optically diffuse and highly reflective surfaces, light sources producing light fluxes of different colors, means for introducing colored light flux from said light sources into said chamber and against certain portions of said surfaces from which scattered multiple reflections occur covering the entire interior sur-, face of said enclosure, said enclosure'having an emission opening therein through which uniformly mixed and diffused light of predetermined spectral contents is emitted. 2. A light'mixer comprising a hollow enclosure in the form of truncated pyramid having an end wall at the" base end thereof and lateral walls connected thereto, said base and walls having interior optically diffuse and highly reflective surfaces, light producing means providing a plurality of light fluxes of different colors impinging upon the interior surface of said enclosure from which scattered multiple reflections occur covering the entire interior surface of said enclosure, said enclosure having an emission opening at the smaller end of said lateral walls through which uniformly mixed 'and diffused light of predetermined spectral contents is emitted.

References Cited in the file of this patent UNITED STATES, PATENTS 

1. A LIGHT MIXER COMPRISING A HOLLOW ENCLOSURE IN THE FORM OF A TRUNCATED PYRAMID HAVING AN END WALL AND LATERAL WALL CONNECTED THERETO DEFINING A MIXING CHAMBER, SAID WALLS HAVING INTERIOR OPTICALLY DIFFUSE AND HIGHLY REFLECTIVE SURFACES, LIGHT SOURCES PRODUCING LIGHT FLUXES OF DIFFERENT COLORS, MEANS FOR INTRODUCING COLORED LIGHT FLUX FROM SAID LIGHT SOURCES INTO SAID CHAMBER AND AGAINST CERTAIN PORTIONS OF SAID SURFACES FROM WHICH SCATTERED MULTIPLE REFLECTIONS OCCUR COVERING THE ENTIRE INTERIOR SURFACE OF SAID ENCLOSURE, SAID ENCLOSURE HAVING AN EMISSION OPENING THEREIN THROUGH WHICH UNIFORMLY MIXED AND 